Embedded packaging for high voltage, high temperature operation of power semiconductor devices

ABSTRACT

Embedded packaging for high voltage, high temperature operation of power semiconductor devices is disclosed, wherein a semiconductor die is embedded in a dielectric body comprising a dielectric polymer composition characterized by a conductivity transition temperature Tc, a first activation energy EaLow for conduction in a temperature range below Tc, and a second activation energy EaHigh for conduction in a temperature range above Tc. A test methodology is disclosed for selecting a dielectric epoxy composition having values of Tc, EaLow and EaHigh that provide a conduction value below a required reliability threshold, e.g. ≤5×10−13 S/cm, for a specified operating voltage and temperature. For example, the power semiconductor device comprises a GaN HEMT for operation at &gt;100V wherein the package body is formed from a laminated dielectric epoxy composition for operation at &gt;150 C, wherein Tc is ≥75 C, EaLow is ≤0.2 eV and EaHigh is ≤1 eV, for improved reliability for high voltage, high temperature operation.

CROSS-REFERENCE TO RELATED APPLICATION(S)

n/a

TECHNICAL FIELD

This invention relates to embedded packaging for power semiconductordevices, such as Gallium Nitride (GaN) High Electron MobilityTransistors (HEMTs), for high voltage and high temperature operation,and test methodologies for assessing materials systems for embeddedpackaging of power semiconductor devices.

BACKGROUND

GaN power transistors, such as GaN HEMTs, provide for high current, highvoltage operation combined with high switching frequency. For some powerapplications, GaN power devices and systems offers advantages oversilicon technology using Si IGBTs and diodes and SiC power transistorsand diodes. For example, power switching systems comprising lateral GaNtransistors provide higher efficiency switching, with lower losses, andsmaller form factor than comparable systems based on silicon or SiCtechnology. To benefit from the inherent performance characteristics oflateral GaN transistors, important design considerations include, e.g.:device layout (topology), low inductance interconnect and packaging, andeffective thermal management. Lateral GaN power transistors for highcurrent operation at 100V and 650V operation are currently availablefrom GaN Systems Inc. based on Island Technology® that provides a largegate width W_(g), low on-resistance, R_(on), and high current capabilityper unit active area of the device.

Packaging solutions that offer low inductance interconnections, andeither top-side or bottom-side thermal pads, are disclosed, for example,in the Applicants earlier filed patent applications: U.S. patentapplication Ser. No. 15/027,012, filed Apr. 15, 2015, now U.S. Pat. No.9,659,854, entitled “Embedded Packaging for Devices and SystemsComprising Lateral GaN Power Transistors”; U.S. patent application Ser.No. 15/064,750, filed Mar. 9, 2016, now U.S. Pat. No. 9,589,868,entitled “Packaging Solutions for Devices and Systems Comprising LateralGaN Power Transistors”; U.S. patent application Ser. No. 15/064,955,filed Mar. 9, 2016, now U.S. Pat. No. 9,589,869, entitled “PackagingSolutions for Devices and Systems Comprising Lateral GaN PowerTransistors”; and U.S. patent application Ser. No. 15/197,861, filedJun. 30, 2016, now U.S. Pat. No. 9,824,949, entitled “PackagingSolutions for Devices and Systems Comprising Lateral GaN PowerTransistors”.

The above referenced patents disclose examples of “embedded packaging”in which the GaN die is embedded in a dielectric package body, e.g.: adielectric polymer resin composition, such as a plastic encapsulationmaterial or a glass fiber epoxy composite, such as FR4 type materials,or a ceramic composite material. Conductive interconnects through thedielectric layers are provided e.g., by copper traces, posts and vias,that provide low inductance interconnections to external contact pads(lands) for source, drain and gate connections. In some types ofencapsulated packaging, the GaN die is embedded by overmolding orinjection of a polymer dielectric material around the die and conductiveinterconnect materials. Alternatively, the dielectric body of laminatedpackaging for embedded GaN dies may be built up from layers ofdielectric materials, e.g. as described in Application Note GN002entitled “Thermal Design for GaN Systems' Top-side cooled GaNPx®-Tpackaged devices” (30 Oct. 2018 GaN Systems Inc.). This type oflaminated packaging provides low parasitic inductance in compact (i.e.small form factor) package for high voltage, high current GaN e-HEMTs.For example, a 100V, 90 A GaN e-HEMT (GS61008T) may be provided in atop-side cooled laminated package which is about 7 mm×4 mm, and 0.54 mmthick; a 650V, 60 A GaN e-HEMT (GS66516T) may be provided in a laminatedpackage which is 9 mm×7.6 mm and 0.54 mm thick.

The dielectric polymer resin composition forming laminated packaging mayinclude laminate sheets and layers of composite material referred to asprepreg, which is a substrate material, such as woven or non-wovenglass-fiber cloth, that is pre-impregnated with one or more polymermaterials, such as a dielectric epoxy composition. The dielectric epoxycomposition may comprise an epoxy resin, curing agents, additives, suchas fire retardants, and fillers and other substances to modifyproperties of the resulting composite material. The epoxy laminate andprepreg layers are cut to form a cavity for the semiconductor die, andthe layers are assembled as a stack and bonded together, e.g. in acuring process using heat and pressure, to form a dielectric body of thepackage in which the semiconductor die is embedded.

A wide range of different dielectric polymer resin compositions, e.g.epoxy laminate and prepreg materials, are commercially available andwidely used for semiconductor device packaging. Materials systems fordielectric epoxy compositions fabricated from glass fibers and cureddielectric epoxy resins are well characterized with respect tothermo-mechanical and thermo-chemical properties and curing processes.For example, specification sheets may list properties such as glasstransition temperature (Tg), coefficient of thermal expansion (CTE),flexural modulus, water absorption, dielectric constant, et al., whichare evaluated according to industry standard test methods. By way ofexample, laminate and prepreg materials may be classed by theirsuppliers as high Tg, high or low elastic modulus, high or low CTE,halogen-free, et al. The use of these types of dielectric materials forlaminated/embedded packaging for semiconductor devices for reliable longterm operation at lower voltage and lower temperatures is wellestablished. Package design consideration for low inductanceinterconnect and thermal dissipation are also well understood.

GaN power switching devices, such as those mentioned above offered byGaN Systems Inc., which are embedded in a GaNPX type laminated packageof small size, e.g. e.g. 7 mm×5 mm and 0.5 mm thick, are capable ofoperation at voltages in a range from 100V to 650V, for switchingcurrents of tens or hundreds of Amps. Operating temperatures may reachor exceed 100 C. For small size dies having a high current capabilityper unit active area, and smaller package sizes, e.g. chip-scalepackaging, package components are therefore subjected to higher electricfields and higher operating temperatures than for low voltage, lowerpower switching devices.

It is known that some dielectric epoxy-based materials systems aresusceptible to degradation when subjected to high electric fields,especially at elevated operating temperatures. This reliability issuepresents a challenge when selecting dielectric epoxy materials forembedded packaging of high voltage/high current GaN e-HEMT powerswitches, that operate at high voltages and high temperatures, wherehigh voltages combined with small geometry dies and packages result incomponents being subject to high electric fields. In seeking suitabledielectric materials for improved reliability for operation at highvoltages, e.g. for GaN HEMTs operating in the range from 100V to 650V,and operating temperatures ≥100 C, the inventor has become aware thatlong term reliability issues resulting from degradation at high electricfield and high temperature of commonly used epoxy materials are not wellunderstood. There is a need for alternative or improved materialssystems and test and design approaches for fabrication of embeddedpackaging of power switching devices, that extend reliable operation forat least one of higher operating temperature, higher voltage operation,and smaller geometry designs for more dense packaging and lower cost.

In particular, there is a need for improved or alternative packaging forhigh voltage/high current power semiconductor devices, such as GaNHEMTs, that provides improved reliability for high voltage and hightemperature operation.

SUMMARY OF INVENTION

The present invention seeks to provides improved or alternativepackaging for wide-bandgap semiconductor power devices, such as GaNHEMTs and SiC power MOSFETS, and a test and design methodology, whichmitigate or circumvent at least one of the above-mentioned issues.

A first aspect of the invention provides a semiconductor devicecomprising: a package comprising a dielectric body;

a semiconductor die embedded in the dielectric body of the package;the semiconductor device being rated for at least one of an operatingvoltage V>100V and operating temperature T≥100 C, whereinthe dielectric body comprises a polymer resin composition characterisedby:

-   -   a conduction transition temperature Tc,    -   a first (low temperature) activation energy Ea_(Low) for        conduction in a first temperature range below Tc,    -   a second (high temperature) activation energy Ea_(High) for        conduction in a second temperature range above Tc;        and    -   the polymer composition having values of Tc, Ea_(Low), and        Ea_(High) that provide a conductivity less than a specified        reliability threshold value of conduction for the rated        operating voltage and operating temperature.

The values of Tc, Ea_(Low) and Ea_(High) are determined frommeasurements of leakage current or conduction as a function oftemperature and voltage for a sample of the dielectric polymercomposition, e.g. having dimensions similar to the dielectric body ofthe package for a power semiconductor die, such as a GaN on silicon diecarrying a GaN e-HEMT, which is rated for a specific operating voltage,e.g. 100V or 650V, and an operating temperature of e.g. ≥100 C or >150C.

For example, the dielectric polymer composition is an epoxy composition,which may be a laminated epoxy composition. Alternatively, the polymercomposition may be a polyimide composition or other type of dielectricpolymer composition.

For example, for a package body comprising a laminated epoxycomposition, the specified reliability threshold for conduction at anoperating voltage of 100V and an operating temperature of 150 C may beset at less than 2×10⁻¹³ S/cm, and preferably less than 5×10⁻¹⁴ S/cm.For example, this may correspond to a leakage current at 150 C of lessthan 3×10⁻⁸ A/cm², or preferably less than 3×10⁻⁹ A/cm².

The first (low temperature) activation energy Ea_(Low) is selected to beless than a specified first threshold activation energy, which is closeto zero, e.g. ≤0.5 eV, and preferably ≤0.2 eV. Where Tc is greater thanthe rated operating temperature, any increase in conduction over theoperating temperature range will be determined by Ea_(Low). Thus,selection of an epoxy laminate composition having a high Tc, greaterthan the operating temperature and small value of Ea_(Low) will maintainconduction below the required reliability threshold.

If the Tc is above the rated operating temperature, conduction attemperatures above Tc will be determined by Ea_(High). If the value ofEa_(High) is high, conduction will increase rapidly with temperatureabove Tc. It is therefore desirable that the second (high temperature)activation energy Ea_(High) is less than a specified second thresholdactivation energy, e.g. ≤1 eV, or preferably less than 0.75 eV, tomaintain the conduction below the required reliability threshold.

Where there is a sharp transition from a low temperature conductionregion to a high temperature conduction region, Tc is well defined.Thus, a laminate epoxy composition having appropriate values of Tc,Ea_(High) and Ea_(High) that maintain conduction below the reliabilitythreshold up to the maximum operating temperature is selected.

The power switching device may comprise a lateral GaN power transistor,for example, a lateral GaN e-HEMT rated for 100V operation or 650Voperation. Alternatively, the power switching device may comprise a SiCMOSFET or a Si IGBT or a diamond power MOSFET.

Another aspect of the invention provides a semiconductor devicecomprising:

a package comprising a dielectric body;a power semiconductor die comprising a power transistor switch embeddedin the dielectric body of the package with electrical connectionsextending to external source, drain and gate contact areas of thepackage,the power transistor switch being rated for an operating voltage V≥100Vand an operating temperature T≥100 Cwherein, the dielectric body comprises a polymer resin compositioncharacterised by:

-   -   a conduction transition temperature Tc,    -   a first (low temperature) activation energy Ea_(Low) for a first        temperature range below Tc,    -   a second (high temperature) activation energy Ea_(High) for a        second temperature range above Tc; and        wherein the values of Tc, Ea_(High) and Ea_(High) provide a        conductivity (S/cm) less than a reliability threshold value of        conduction for the rated operating voltage and temperature of        the power transistor switch.

For example, the dielectric polymer composition that forms thedielectric body of the package is a laminated epoxy composition, andelectrical connections comprise copper.

In some embodiments, the power switching device comprises a lateral GaNpower transistor, e.g. a high current lateral GaN e-HEMT which is ratedfor operation up to 100V, or for operation up to 650V.

For example, in some embodiments, the epoxy composition is selected toprovide a reliability threshold for conduction ≤2×10 ⁻¹³ S/cm, orpreferably ≤5×10⁻¹⁴ S/cm, and to provide leakage ≤3×10⁻⁸ A/cm², andpreferably ≤3×10⁻⁹ A/cm². For example, to stay below these thresholds,the first activation energy Ea_(Low) is a specified first thresholdactivation energy of ≤0.2 eV and the second activation energy Ea_(High)is a specified second threshold activation energy of ≤1 eV. Theconductivity transition temperature Tc is preferably high, e.g. ≥100 Cor ≥150 C.

Where Tc is greater than the rated operating temperature, Ea_(Low) has alow value, e.g. ≤0.2 eV that maintains the conduction below thereliability threshold.

Where Tc is less than the rated operating temperature, Ea_(Low) has alow value, e.g ≤0.2 eV, and EaHigh has a value, e.g. ≤1 eV, and morepreferably ≤0.75 eV to maintain the conduction below the reliabilitythreshold.

Also provided is a method of characterizing dielectric polymercompositions for use in packaging of power semiconductor devices forhigh voltage, high temperature operation, comprising:

providing a test sample;for each of a set of temperatures, applying an electric field (V/cm)over a range of operating values and measuring a leakage current (A) asa function of electric field;from said data, for a specified operating voltage V of the powersemiconductor device, generating values of ln(Conduction) vs. q/kT, andfrom the gradient of ln (Conduction vs. q/kT obtaining values of:

-   -   a conduction transition temperature Tc,    -   a low temperature activation energy Ea_(LT) for the first range        of operating temperatures below Tc,    -   a high temperature activation energy Ea_(HT) for the second        range of operating temperatures above Tc.

Since local electric fields are dependent on package geometry andinterconnect structure, providing a test sample comprises providing asample of the laminated dielectric composition having dimensions (e.g.length (x), width (y) and thickness (z) dimensions) commensurate with asemiconductor package to be fabricated, or providing a packaged die fortesting.

The method may further comprise, for a said specified operating voltageV and operating temperature T of the power semiconductor device,assessing whether the dielectric polymer composition meets a reliabilitythreshold for conduction. For example, for a package body comprising alaminated epoxy composition, the reliability threshold for conduction atan operating voltage of 100V and an operating temperature of 150 C maybe set at less than 2×10 ⁻¹³ S/cm, and preferably less than 5×10⁻¹⁴S/cm, which may correspond to a leakage current at 150 C of less than3×10⁻⁸ A/cm², or preferably less than 3×10⁻⁹ A/cm².

For example, to meet a required reliability threshold for conduction, itmay be specified that the conductivity transition temperature is at orabove the rated operating temperature, and the low temperatureactivation energy Ea_(Low) is less than a specified first thresholdactivation energy, which is close to zero, e.g. ≤0.5 eV, and morepreferably ≤0.2 eV. Where Tc is less than the rated operatingtemperature, it may be specified that the high temperature activationenergy Ea_(High) is less than a specified second threshold activationenergy, e.g. ≤1 eV, or preferably less than 0.5 eV, to maintain theconduction below the reliability threshold for temperatures above Tc.

Where conduction characteristics as a function of electric field andtemperature comprising values of Tc, Ea_(Low) and Ea_(High) are providedfor a plurality of different polymer resin compositions, ranking of thepolymer resins by these conduction characteristics is possible, toassist in selecting appropriate polymer resin compositions to meet arequired reliability threshold of conduction. For example, in a fullycured dielectric polymer composition, such as a dielectric epoxycomposition or a dielectric epoxy laminate composition, the lowtemperature activation energy Ea_(LT) would ideally be close to zero, orvery low. In practice the low temperature activation energy Ea_(LT) isselected to be ≤0.5 eV, preferably ≤0.2 eV, and more preferably ≤0.1 eV.Preferably, the conductivity transition temperature is higher than thespecified maximum operating temperature, or close to the maximumoperating temperature so that conduction is primarily determined myEa_(LT). If the conductivity transition temperature Tc is less than thespecified maximum operating T, it is also required that the hightemperature activation energy Ea_(HT) does not exceed a requiredthreshold value, e.g. is ≤1 eV, or more preferably ≤0.5 eV, becauseconduction above Tc contributes more significantly to leakage current.For example, for operation >100V at an operating temperature of 100 C,it is desirable that the dielectric polymer material has a Tc above 100C, preferably 150 C, and Ea_(LT) is ≤0.2 eV. If, for example, Tc is atleast 70 C or 80 C, then Ea_(HT) is preferably less than 0.5 eV. Forexample, by appropriate selection of these parameters, the conductivityat 150 C is less than 2×10⁻¹³ S/cm, preferably less than 5×10⁻¹⁴ S/cm,and more preferably less than 1×10¹⁴ S/cm.

This test methodology provides for characterizing dielectric polymermaterials, such as dielectric epoxy laminate materials, forsemiconductor device packaging, to facilitate selection of anappropriate dielectric materials system, providing a design approachthat extends reliable operation for at least one of higher operatingtemperatures, higher operating voltage, and to support smallergeometries for more dense packaging and lower cost.

Thus, embodiments of the invention provides for improvements in embeddedpackaging for power semiconductor devices, such as high voltage powerswitching devices comprising e.g. GaN HEMTs, SiC MOSFETs and SiIGBTs,operating at elevated temperatures, and a test methodology for assessingelectrical conduction characteristics of dielectric polymer compositionsfor embedded packaging, for improved device performance and reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3 (Prior Art) shows schematic views of an example of anE-mode GaN HEMT device structure embedded in a laminated epoxy packagewith bottom-side cooling;

FIGS. 4 to 6 (Prior Art) shows schematic views of another example of anE-mode GaN HEMT device structure embedded in a laminated epoxy packagewith top-side cooling;

FIG. 7 shows an example of plots of Leakage Current (A) vs. ElectricField (V/cm), for temperatures in the range 0 C to 200 C, for a sampleof a laminated epoxy dielectric material;

FIG. 8 shows an example of plots of Conduction Jdss (A/cm²) at 520V vs.

Temperature for six samples of laminated epoxy dielectric material;

FIG. 9 shows a schematic example of an Arrhenius type plot of thenatural log of the conduction Ln(Conduction) vs. q/kT for a sample oflaminated epoxy material to determine a conductivity transitiontemperature Tc, and activation energies Ea_(Low) and Ea_(HIGH) for highand low temperature operating regimes;

FIG. 10A shows a schematic diagram of a cross-linked polymer network forconduction at low temperature, and FIG. 10B shows a schematic diagram ofa cross-linked polymer network for conduction at high temperature; and

FIG. 11 shows a schematic plot of Ln(Conduction) vs. q/kT for a firstexample scenario;

FIG. 12 shows a schematic plot of Ln(Conduction) vs. q/kT for a secondexample scenario;

FIG. 13 shows a schematic plot of Ln(Conduction) vs. q/kT for a thirdexample scenario;

FIG. 14 shows a schematic plot of Ln(Conduction) vs. q/kT for a fourthexample scenario;

FIG. 15 shows a schematic plot of Ln(Conduction) vs. q/kT for a fifthexample scenario;

FIG. 16 shows a table of experimental data obtained for samples of someexemplary epoxy laminate materials;

FIG. 17 shows a plot ranking the samples by activation energies Ea_(Low)and Ea_(High);

FIG. 18 shows a corresponding comparison of Tc for each sample;

FIG. 19 shows a corresponding comparison of conductivity S/m @150×10E14for each sample; and

FIG. 20 shows a corresponding comparison of Leakage A/cm² @150 C×10E8for each sample.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription, taken in conjunction with the accompanying drawings, ofpreferred embodiments of the invention, which description is by way ofexample only.

DETAILED DESCRIPTION

Examples of embedded packaging device structures comprising a laminateddielectric package body containing a lateral GaN power transistor areshown schematically in FIGS. 1 to 6 (Prior Art).

FIG. 1 shows top-side and bottom-side views of a first example of apackage comprising an embedded GaN-on-Si die comprising a 650V lateralGaN e-HEMT. The back-side of the package comprises a thermal pad, andsource, drain and gate contact pads. FIG. 2 shows a simplified schematiccross-sectional view through the package showing the embedded die andpackaging components. FIG. 3 shows an exploded view of the components ofthe package, to illustrate how the GaN-on-silicon die is embedded withina dielectric body of the package which comprises an epoxy compositionfabricated from laminations comprising several epoxy laminate andprepreg layers. The GaN die comprises a thick copper redistributionlayer (RDL) defining large area source, drain and gate contact areas,and a thermal pad. Other components comprise low inductance conductivecopper interconnects comprising copper filled vias, copper filledmicro-vias, and external source, drain and gate pads.

FIG. 4 shows top-side and bottom-side views of another example of apackage comprising an embedded GaN-on-Si die comprising a GaN e-HEMT.The front side of the package comprises a thermal pad. Source, drain andgate pads are provided on a back-side of the package. FIG. 4 shows asimplified schematic cross-sectional view through the package showingthe embedded die and packaging components with the thermal pad on top.FIG. 5 shows an exploded view of the components of the package, whichshows how the GaN die is embedded in a dielectric package bodycomprising laminations of several epoxy laminate/prepreg layers, withthe copper thermal pad and thermally conductive copper filledmicro-vias, and electrically conductive copper interconnects comprisinglow inductance copper filled vias and external source, drain and gatepads.

The fabrication process for this type of embedded component package isbased, for example, on the AT&S ECP® and Centre Core ECP® processes. Thepackage is fabricated by placing each GaN die in a cavity within a stackof layers, comprising epoxy laminate/prepreg, and curing the epoxylaminate composition so that the GaN die is embedded in a soliddielectric body. The electrical connections to the GaN die are formed insubsequent steps, e.g. by drilling micro-vias and through-substratevias, which are then filled with plated copper, to form low inductanceelectrical interconnections. Copper filled micro-vias provide a thermalconnection from the back-side of the die to the thermal pad.

Since these packages are small in size, e.g. ˜10 mm×˜5 mm and about 0.5mm thick, for operation at high voltages, e.g. at 100V or 650V, thedielectric body of the package, i.e. comprising the epoxy laminations,is subjected to high electric fields during operation. Conventionallower cost epoxy materials, e.g. FR4 type epoxy materials containinghalogens as flame retardants, are susceptible to degradation under highelectric fields, particularly at higher operating temperature. Forexample, degradation may be observed in the form of corrosion of coppercontacts caused by migration of halogen ions, such as chlorine orbromine.

Package design considerations for low inductance interconnect andthermal dissipation are well understood, and the thermo-mechanicalproperties of epoxy materials systems for laminated packaging are wellcharacterized, by industry standard test methods, so that appropriateepoxy materials can be selected based on parameters such as Tg, CTE, etal., that are reported on materials specification sheets. Thus,appropriate epoxy laminates and prepregs for laminated packaging may beselected based on these parameters, e.g. to optimize thermal andmechanical performance. The specified parameters may include electricalparameters including dielectric constant (Dk) and dissipation factor(Df) at a specified frequency or frequencies, resistivity, and surfaceresistance. However, in seeking suitable materials for packaging powerswitches comprising GaN e-HEMTs operating at ≥100V or ≥650V, it hasbecome apparent that the performance of dielectric epoxy materialssystems under high electric fields, particularly at higher operatingtemperatures, is not well characterized or understood. Specificationsheets and standard test methods for epoxy composite materials forlaminated packaging do not report other parameters that would assist inselecting dielectric materials systems that are optimized for highvoltage and high temperature operation of embedded power devices,particularly where a package of small dimensions results in thedielectric materials of the package being subject to high electricfields, e.g. in a range of ˜10³V/cm to 10⁵V/cm. Thus, for high voltageand high temperature operation, selection of appropriate epoxy materialssystems, or other suitable dielectric materials systems, for laminatedpackaging has been based, in part, on trial and error. It will also beapparent that, for a specified operating voltage and operatingtemperature, in practice, the electric field experienced by thedielectric material of the package is dependent on, or influenced by,factors such as the size and geometry of the package body, and the sizeand layout of the die and conductive interconnect structure.

Disclosed herein is a test methodology for assessing the performance ofdielectric polymer materials, such as epoxy composite materials systems,for fabrication of embedded packaging, including laminated packaging, ofpower semiconductor devices that operate at high voltages and highcurrents, and at elevated operating temperatures. This test methodologyis based on measurements of leakage current (A/cm²) as a function ofelectric field and temperature, that provides parameters comprising aconductivity transition temperature Tc, and first and second activationenergies, Ea_(Low) and Ea_(High), where Ea_(Low) is for conduction in afirst temperature range below Tc, and Ea_(High) is for conduction in asecond temperature range above Tc. The conductivity transitiontemperature Tc, and the first and second activation energies, Ea_(Low)and Ea_(High) can be used to rank materials and assist in selectingappropriate dielectric materials for embedded packaging. As an example,the method is described for selecting materials comprising dielectricepoxy compositions for laminated packaging of power semiconductordevices, such as GaN e-HEMTs, that operate at high voltage and highcurrent, resulting in higher operating temperatures than typical for lowpower and low voltage semiconductor devices, and resulting in exposureto higher electric fields than for low power semiconductor devices.

Test Methodology

Test samples of laminated epoxy dielectric materials having dimensionstypical of the size of packaged GaN HEMTs shown in FIGS. 1 to 6,embedded between copper electrode layers were obtained. For each sample,an electric field was applied in the Z direction, i.e. across thethickness of the sample, and a series of measurements of the leakagecurrent (A) vs. electric field (V/cm) were made for temperatures in arange of 0 C to 200 C, and for electric fields in the range from 0V/cmto over 10⁵V/cm. In an embodiment, the sample was connected to acomputer controlled power supply and placed into a temperaturecontrolled environment. A temperature was selected and after the samplestabilized or came into thermal equilibrium, the power supply voltagewas swept from 0V to 650V in 5V steps and the total current was measuredat each bias point.

For example, FIG. 7 shows an example of plots of Leakage Current (A) vs.Electric Field (V/cm), for temperatures in the range 0 C to 200 C, forone sample of a laminated epoxy material. The leakage current increaseswith electric field and temperature.

FIG. 8 shows an example of plots of conduction Jdss (A/cm²), for anapplied voltage of 520V, for six samples of laminated epoxy materialwhich are cured to the Soft Lamination Stage (SLS). There is anon-linear increase in Jdss with temperature.

FIG. 9 shows a schematic Arrhenius type plot of data for one sample,which is a plot of the natural logarithm of the conduction,Ln(Conduction) against q/kT, wherein T is the temperature in Kelvin, qis the electron charge 1.602×10⁻¹⁹ C, and k is the Boltzmann constant,for determining activation energies in eV. The slope of the plot ofLn(J) vs. 1/t is used to obtain an activation energy, in eV, forconduction for different temperature ranges.

As illustrated schematically in FIG. 9, for the samples tested, it wasobserved that the conduction shows a distinct transition between a lowtemperature conduction region and high temperature conduction region.Activation energies for the low temperature conduction region and hightemperature conduction region are determined from gradient of eachregion of the plot of Ln(J) vs 1/T, as shown. The sample epoxy laminatecompositions exhibit two conduction modes, with a first activationenergy Ea_(Low) over a first (lower) temperature conduction range and asecond activation energy Ea_(High) over a second (higher) temperatureconduction range, and a transition region between the two. Thetransition point is referred to as the conductivity transitiontemperature, Tc, and marks a change in conduction mechanism as thetemperature is increased.

FIGS. 10A and 10B show schematic representations of a cross-linked epoxypolymer network at first and second temperatures to illustrateconduction under a high electric field for a low temperature conductionregime and a high temperature conduction regime. Without wishing to belimited by theory, the following is believed to provide a possibleexplanation of the conductivity transition from a low temperatureconduction region below Tc to a high temperature conduction region aboveTc.

Low Temperature Conduction

Low temperature conduction in dielectric epoxy compositions (“epoxy”) isdue to electrons associated with the cross-linking of the cured epoxy.At low temperatures with fully cured epoxy there is a dense network ofcross-linking of the epoxy molecules, with a full valance band. Thissituation should define a good insulator with very little current flow.Due to the nature of organic epoxies not all of these cross-linkingmolecules are linked and shallow traps or defects are formed. When abias is applied a small leakage current flows and the temperaturedependence of the current flow is due to the shallow traps. Theseshallow traps result in a low activation energy, e.g. <0.5 eV or closeto zero, for conduction in the low temperature regime, as illustrated bythe smaller gradient in the low temperature region of the plot in FIG.9.

As illustrated schematically in FIG. 10A, at lower temperatures theepoxy matrix is dense and atomic bond length is small, e.g. ˜150 pm.Electron conduction can occur along atomic bonds. However, if additivessuch as a halogen are added for flame resistance, a halogen ion such asa chorine Cl⁻ ion is large ˜180 pm in diameter, and interstitialconduction is limited by the shaded area between atoms.

High Temperature Conduction

As the temperature is increased, the epoxy matrix starts to expand dueto CTE, the density of the epoxy decreases. This is accompanied by anincrease in leakage current for a fixed bias with increasingtemperature. The higher temperature conduction is more dependent ontemperature and the leakage currents can quickly grow. This region has ahigher activation energy as illustrated by the steeper gradient of theplot in the high temperature conduction region of FIG. 9.

For a high voltage embedded power package an increase in current underhigh electric field at higher temperature represents a reliabilityissue. This issue is due to the damaging effect of hot electrons thatare flowing through the epoxy, e.g. releasing unwanted hydroxyls,halogens and other impurities from the epoxy. To further improve theperformance of epoxy at high temperatures and high applied voltages,dielectric fillers such as silica SiO₂ and alumina Al₂O₃ are used. Thesefillers are small and spherical in shape and have the effect ofincreasing the path length for any leakage current that might flow.Thus, as illustrated schematically in FIG. 10B, at high temperatures theepoxy matrix is less dense and atomic spacing is larger. Electronconduction can still occur along atomic bonds. However, ionic conductionis no longer limited by the shaded area between atoms and ions are freeto move under an electric field.

Package Leakage Current

Dielectric polymer resin compositions, such as dielectric epoxycompositions, and dielectric epoxy laminate compositions, are known tocontain many additives, e.g. fillers such as silica and alumina, flameretardants, and impurities, e.g. Br, Fe, etc. These impurities can becharged and drift under the applied operating electric field. Forexample, when Cl⁻ ions reach a copper electrode in the package,corrosion of the copper can occur. This corrosion can result in thetransport of Cu⁺ ions back towards the cathode that can eventuallyresult in a dielectric breakdown leading to reliability issues. Forexample, this type of copper corrosion has been shown to be proportionalto the leakage current density in the epoxy composition. To reduce thecopper corrosion or degradation of the epoxy, it is desirable to reducethe available leakage current at high temperatures and high voltages. Byobtaining high temperature and high voltage conduction characteristicsof epoxy materials, it is possible to define parameters Tc, Ea_(Low) andEa_(High), that assist in making an appropriate choice of dielectricepoxy composition materials to maintain leakage currents below areliability threshold.

The following example scenarios show how dielectric epoxy compositionshaving appropriate values of Tc, Ea_(Low) and Ea_(High) can be selectedto maintain leakage current or conduction values below a specifiedreliability threshold, e.g. for corrosion free operation.

Example 1

FIG. 11 shows a schematic plot of Ln(conduction) vs. q/kT for a firstexample of a material in which there is a transition from a lowtemperature conduction region characterized by a first activation energyEa_(Low), below transition temperature Tc, to a high temperatureconduction region characterized by a second activation energy above Tc.If for example, the required operating temperature is T1, where T1=150C, Tc is higher than T1, and Ea_(Low) is small, e.g. ≤0.5 eV or ≤0.2 eV,operation at temperatures below Tc maintains the conduction at a valuewell below a required reliability threshold for conduction, e.g. 3×10⁻¹³ S/cm. Above Tc, the conduction increases more rapidly withtemperature, i.e. dependent on the second activation energy Ea_(High),e.g. 1 eV. In this example, operation at T2 would be close to thereliability threshold for conductions, but falls in the region above Tc,where conduction increases rapidly with temperature above thereliability threshold, e.g. at T3. These characteristics imply that theepoxy material is appropriate for operation at the required operatingvoltage and temperatures ≤T1.

Example 2

FIG. 12 shows a plot of Ln(conduction) vs. q/kT for a second example ofa material in which there is a transition from a low temperatureconduction region characterized by a first activation energy Ea_(Low),below transition temperature Tc, to a high temperature conduction regioncharacterized by a second activation energy above Tc, in which Tc occursat a lower temperature than for Example 1. Ea_(Low) is small, e.g. ≤0.2,and operation at temperatures below Tc maintains the conduction at avalue well below a required reliability threshold for conduction, e.g.3×10⁴³S/cm. However, since Tc is low, e.g. 50 C, conduction increasesmore rapidly with temperature above Tc, i.e. dependent on the secondactivation energy Ea_(High), above Tc. Thus, reliable operation isrestricted to temperatures below T1, and reliability is borderline forT2. This implies that this material would be suitable only for lowertemperature operation at the specified operating voltage.

Example 3

FIG. 13 shows a plot of Ln(conduction) vs. q/kT for a third example of amaterial in which there is a transition from low temperature conductionregion characterized by a first activation energy Ea_(Low), belowtransition temperature a Tc, to a high temperature conduction regioncharacterized by a second activation energy above Tc, in which Tc occursat a high temperature, similar to Example 1. However, in this exampleEa_(Low) is larger, e.g. >0.5 eV, and as the temperature increases, theconduction exceeds the specified reliability threshold at temperaturesbelow Tc. Thus, reliable operation is restricted to temperatures belowT1. This implies that this material would be suitable only for lowertemperature operation at the specified operating voltage.

Example 4

FIG. 14 shows a plot of Ln(conduction) vs. q/kT for a fourth example ofa material in which there is a transition from a low temperatureconduction region characterized by a first activation energy Ea_(Low),below transition temperature Tc, and a high temperature conductionregion characterized by a second activation energy above Tc, in whichthe conductivity transition occurs over a larger conductivity transitionrange, between Tc_(max) and Tc_(min). For example, of Tc is defined inthe middle of this range, and is e.g. 150 C, similar to Example 1.Ea_(Low) is low, so that conduction increases slowly with temperaturebelow Tc mm, and then increases more rapidly in the transition region. Amaximum operating temperature Tmax, close to Tc_(max) maintainsconduction at a value below the required reliability threshold forconduction, e.g. 3×10 ⁻¹³ S/cm. This example implies that this materialwould be suitable for reliable operation at the specified operatingvoltage for temperatures T_(max) close to Tc_(max).

Example 5

FIG. 15 shows a plot of Ln(conduction) vs. q/kT for a fifth example of amaterial in which there is a transition from a low temperatureconduction region characterized by a first activation energy Ea_(Low),below transition temperature Tc, and a high temperature conductionregion characterized by a second activation energy above Tc, in whichthe conductivity transition occurs over a larger conductivity transitionrange, between Tc_(max) and Tc_(min). For example, Tc is defined in themiddle of this range, and is e.g. 100 C, similar to Example 4. However,in this example, Ea_(Low) is larger, so that conduction increases morerapidly with temperature, exceeding the reliability threshold as thetemperature enters the transition range. To maintain the conduction at avalue below the required reliability threshold for conduction, e.g. 3×10⁻¹³ S/cm, the maximum operating temperature Tmax is limited to just overTc_(min).

In principal, there may be many combinations of characteristics Tc,Ea_(Low) and Ea_(High) that can provide reliable high voltage, hightemperature operation so long as the total conductance is maintainedbelow a required threshold value, e.g. approximately 5×10⁻¹³ S/cm at therequired maximum operating voltage and temperature.

By way of example, the Table shown in FIG. 16 lists experimental datafor ten samples, i.e. five dielectric epoxy laminate compositions, foreach of two cures: a SLS (Soft Lamination Stage) cure in which the epoxycomposition is partially cured, e.g. to hold together laminations, and aFL (Full Lamination) cure, in which the epoxy composition is fullycured, i.e. hard lamination. The temperature dependence of leakagecurrent was determined for each of the samples by sweeping the voltageover a range of 0V to 650V, applied in the Z direction, for a set oftemperatures over a temperature range of 0 C to 200 C, to obtain valuesfor Tc (C), the first activation energy Ea_(Low) (eV) and the secondactivation energy Ea_(High) (eV) as described above. Also listed are themeasured values of the conductivity (S/cm) at 150 C and leakage (A/cm²)at 150 C.

Over the measured temperature range, the plots of ln (Conduction) vs.1/kT for each of these samples showed a distinct (sharp) conductiontransition temperature Tc, between a low temperature conduction regioncharacterised by a first activation energy Ea_(Low) and a hightemperature conduction region characterized by a second activationenergy Ea_(High), where Ea_(High) is greater than Ea_(Low), i.e. similarto the form of plots illustrated schematically for the Examples shown inFIGS. 11 to 13. Thus, a distinct conduction transition temperature Tcwas obtained for each sample. In the temperature range tested, none ofthe samples showed a broader conduction transition range as illustratedschematically for the Examples shown in FIGS. 14 and 15.

The plots shown in FIGS. 17 to 20 compare parameters for each samplelisted in the table of FIG. 16. FIG. 17 shows a plot of activationenergies Ea_(Low) and Ea_(High) for the ten samples, ranked in order ofincreasing Ea_(High). FIG. 18 shows a corresponding comparison of Tc foreach sample; FIG. 19 shows a corresponding comparison of conductivity;and FIG. 20 shows a corresponding comparison of leakage.

Referring to FIG. 17, all samples have a low temperature activationenergy Ea_(Low) below 0.5 eV. The high temperature activation energyEa_(High) increases from sample Ref 1 to Ref 5.

Sample DOE7501 (Ref./Rank 1) which comprises a R1577 laminate core andE-770G epoxy prepreg, showed the lowest conductivity, i.e. 4.75×10⁴⁴S/cm for the SLS cure, and 2.27×10⁻¹⁴ S/cm for the FL cure.Corresponding values of leakage for SLS cure and FL cure were 1.06×10⁻⁸A/cm² and 2.9×10⁻⁹ A/cm². These samples also had the lowest values ofEa_(Low) (0.16 eV and 0.09 eV) and Ea_(High) (0.62 eV and 0.67 eV), andconductivity transition temperatures of 75.8 C and 85.6 C respectively.Thus, this combination of characteristics demonstrated that the HitachiR1577/E-770G material to be superior in terms of electrical conductionand other characteristics for use in high voltage, high temperatureembedded packaging comprising an epoxy laminate composition.

Sample DOE7504 (Ref./Rank 2), comprising a R1577 laminate core andHitachi E-679 epoxy prepreg ranks a close second and may prove useful inhigh voltage embedded packaging. This sample had a conductivity of1.8×10⁻¹³ S/cm for the SLS cure, and 1.4×10⁻¹³ S/cm for the FL cure; thecorresponding value of leakage for SLS cure was 2.5×10⁻⁸ A/cm² and1.8×10⁻⁸ A/cm² for FL cure. The values of Ea_(Low) (0.18 eV and 0.16 eV)are close to those of sample DOE7501, and Ea_(High) (0.84 eV and 0.77eV) are higher, and the conductivity transition temperatures of 82.0 Cand 79.7 C are similar to values for DOE7501 (Ref./Rank 1).

In comparison to Sample DOE7501 (Ref./Rank 1) and Sample DOE7504(Ref./Rank 2), the other epoxy compositions exhibit higher values ofEa_(High), and significantly higher values of conductivity and leakage.

For sample ref./rank 4, EaLow is below 0.5 eV and EaHigh is around 1 eV;however, Tc is the lowest of this group of samples, around 50 C. Thus,for operation at 100 C to 150 C, well above Tc, the higher value ofEaHigh results in high conductivity and leakage. For example, for sampleref./rank 5, Ea_(Low) is less than 0.4 eV, and Tc is high, but sinceEa_(High) is >1 eV, for operating temperatures over the Tc of 80 C, thehigh value of Ea_(High) results rapidly increasing conductivity andleakage with temperature. Sample ref./rank 3 fall in between. Based onthese parameters, the performance of samples ref. 1 and 2 is superiorfor high temperature and high voltage operation, e.g. for highvoltage/high temperature power semiconductor devices, such as GaN HEMTsoperating at ≥100V and ≥100 C.

By comparison, samples ref. 3 to 5 are not suitable for thisapplication. At 150 C, each of these epoxy compositions exhibitssignificantly higher conductivity, i.e. >10⁻¹² S/cm, and leakage, i.e.>10⁻⁷ A/cm² at 150 C, higher Ea_(Low) values in a range from 0.29 eV to0.4 eV and Ea_(High) values in a range from 0.81 eV to 1.5 eV. Theconductivity transition temperatures Tc of samples DOE7502 and DOE7503are low, in the range 47.1 C to 69 C. Although sample DOE7500 has a highconductivity transition temperature, 79.0 C for SLS cure and 80.8 C forFL cure, the higher values of Ea_(Low), and particularly the highervalues of Ea_(High) lead to higher values of conductivity and leakage at150 C.

In principal, to select an appropriate epoxy composition, there can bemany combinations of Tc, Ea_(High) and Ea_(High) characteristics thatcan work, so long as the total conductance is less than a requiredthreshold value, e.g. ≤5×10-13 S/cm, or preferably ≤5×10⁻¹⁴ S/cm, at themaximum operating voltage and temperature.

Based on these experimental results, it is possible to provideguidelines for selecting an epoxy with a combination of values ofparameters comprising conductivity, leakage, first and second activationenergies, that can provide a reliable material for an embedded packagefor high voltage operation at ≥150 C of power semiconductor devices.

Firstly, the low temperature conduction characteristics should exhibitan activation energy Ea_(Low) that is low, e.g. ≤0.2 eV and preferablycloser to zero. A low activation energy for the low temperatureconduction range implies a well cured epoxy composition with densecross-linking, which is suitable for embedded packaging applications. IfTc is high, and the operating temperature is below Tc, a high Tc incombination with a first activation energy Ea_(Low) which is close tozero, e.g. ≤0.2 eV, is expected to provide a conductivity below arequired threshold value, e.g. of 5×10⁻¹³ S/cm.

If Tc is below the maximum operating temperature, the high temperatureconduction characteristics are more important, because conductionincreases more rapidly with temperatures over Tc. To maintain theconductivity below the reliability threshold, the second activationenergy Ea_(High) for temperatures above Tc, should be ≤1.0 eV, andpreferably below 0.75 eV. For example, for Tc≥70 C, or Tc≥80 C, orTc≥100 C, for an operating temperature above Tc, it is important thatEa_(High) is small enough to maintain conduction below the reliabilitythreshold of conduction in the operating temperature range above Tc.

The data shown in the Table in FIG. 16 provide examples to assist inquantifying values of Tc, Ea_(Low) and Ea_(High), conduction and leakagefor some samples of commercially available epoxy laminate compositionsto assess suitability for high voltage and high temperature operation.These data are provided by way of example only for these materialssystems. For other dielectric polymer compositions and otherapplications, the minimum achievable leakage current and conductionvalues may fall within other ranges. However, this test methodologyallows for comparison of different materials, e.g. by comparison andranking of Tc, Ea_(Low) and Ea_(High), conduction and leakage, to assistin selecting an appropriate material system for improved reliability,e.g. for at least one of high temperature operation and high voltageoperation, particular when small die size and compact packaging resultsin operation under high electric fields and temperatures ≥100 C.

This test methodology also provides for testing of the homogeneity ofthe dielectric composition and effectiveness of curing of dielectriccomposite materials for embedded packaging. For example, for an ECPprocessing, batch processing provides for embedding of an array of manydie in large sheets of dielectric laminate and prepreg layers. Theselarge sheets are then drilled to form micro-vias and through substratevias, which are filled with plated copper to form electricalinterconnects and thermal interconnects. For example, it is well knownthat, for uniformity of laminate sheets and prepreg layers, there is aneed for a correct stoichiometric mix of resin to hardener. Since epoxycomposite dielectrics also contain dielectric fillers and otheradditives, any incomplete mixing may result in inconsistent materialproperties across a batch of embedded die packages.

A non-uniform mix may result in inhomogeneities across the sheets oflaminate and prepreg, leading to inconsistencies in curing, withdifferent degrees of cross-linking. For operation under high temperatureand high voltage, inconsistencies in composition and curing mayadversely affect conduction and leakage. For embedded die packing ofhigh current, high voltage power semiconductor devices, a proposedapproach is to provide test structures distributed across in each sheet,so that in each batch, several test structures can be tested for Tc,EaLow, EaHigh, conduction and leakage to verify the dielectric meetsspecifications for the rated operating voltage and temperature of theembedded die. This test methodology may also be useful in providingadditional electrical parameters for evaluating the effectiveness ofcure processes, e.g. single stage or multistage cure processes forembedded packaging. For example, some processes for curing epoxylaminate materials use with a multi-stage cure, e.g., an initial partialcure or soft lamination to bond layers, which results in partialcross-linking, partially locking in the structure, followed by full cureto increase cross-linking and fully harden the dielectric layers.Measurements of Tc, EaLow, EaHigh, conduction and leakage for samples ofdielectric polymer compositions processed with different mixing andpreparation steps, and different cure processes may assist withformulation of dielectric polymer compositions and curing processes tooptimize electrical properties of dielectric materials for embeddedpackaging of power semiconductor devices for operation at hightemperature and high voltage, particularly for chip-scale packaging,where the small dimensions of the package result in high electricfields.

For the materials tested, the measured conductivity transitiontemperatures Tc occur below the glass transition temperature for thesematerials. At this time, further work is required to determine if thereis a correlation between the conductivity transition temperature Tc andthe glass transition temperature Tg and other mechanical properties suchas CTE, elastic modulus, et al. of the dielectric materials which weretested.

The device structures and test methodology disclosed herein areapplicable to providing improved reliability for embedded packaging andlaminated packaging of lateral GaN power switches such as GaN HEMTs andother nitride semiconductor devices, such as power switching devices andsystems comprising nitride power transistors which more generallycomprise III-Nitride semiconductors of other compositions, and also forpower switching devices comprising Si and SiC switching devices, e.g.high voltage Si IGBTs and SiC power transistors for operation atvoltages in the range from 100V to 1700V. For example, for variousapplications, switching systems may be provided for one of ≥100Voperation; 300V to 400V operation; ≥600V operation; and ≥1200Voperation.

Selection of appropriate dielectric epoxy compositions for laminatedpackages, to meet a reliability threshold for leakage and conduction,enables more reliable high voltage operation (>100V) at high temperature(>100 C), to assist in achieving a long lifetime without performancedegradation, even with small geometry layouts and small package sizes.While experimental results are disclosed for some exemplary dielectricepoxy compositions, it is expected that the test methodology may beextended to evaluating other dielectric polymer compositions for use insemiconductor packaging for high voltage and high temperature powersemiconductor switching devices, such as GaN e-HEMTs.

The test methodology disclosed herein provides an improved understandingof the effects of temperature and electric field on electricalconduction characteristics of the dielectric epoxy compositions formingthe dielectric body of a semiconductor package, and how the dielectricmaterial interacts with the bias on a semiconductor die embedded intothe dielectric body of the package. It is demonstrated that dielectricepoxy compositions can be characterized by a conductivity transitiontemperature Tc, a first activation energy for conduction at temperaturesbelow Tc, and a second activation energy for conduction at temperaturesabove Tc. Characterization of existing epoxy compositions to identifymaterials having a high conductivity transition temperature, preferablyabove the rated operating temperature, and low first activation energyfor conduction below Tc, enables selection of dielectric epoxycomposition which provide improved reliability for high temperature andhigh voltage operation. Improved understanding of the effects oftemperature and electric field on epoxy compositions may also assist informulation of materials having a higher conductivity transitiontemperature Tc, e.g. >100 C or >150 C, and low conductivity over therequired operating temperature range, while still achieving the othermaterials characteristics needed for volume manufacture forsemiconductor packaging. Where Tc is below the operating temperature,selection of materials having a smaller activation energy for conductionabove Tc, allows for conductivity in the operating range above Tc to bemaintained below a reliability threshold. For example, for the sampledata shown in FIG. 16, samples DOE7501 and DOE7504, having a Tc in arange of 70 C to 90 C, e.g. >75 C, combined with a high temperatureactivation energy Ehigh below 1.0 eV, and preferably below 0.75 eV,showed significantly lower conductivity and leakage than the othersamples. These data also assist in designing packaging for highvoltage/high current power switching devices, e.g. for optimizingconductivity and operating field strength, which based on voltage andgeometry of the package, to minimize degradation over the productlifetime, and to further optimize device performance.

While device structures and methods of embodiments have been describedin detail, with examples of values of Tc, EaLow, EaHigh, conduction andleakage, these are provided by way of example only.

Although embodiments of the invention have been described andillustrated in detail, it is to be clearly understood that the same isby way of illustration and example only and not to be taken by way oflimitation, the scope of the present invention being limited only by theappended claims.

1. A semiconductor device comprising: a package comprising a dielectricbody; a semiconductor die embedded in the dielectric body of thepackage; the semiconductor device being rated for operation with atleast one of an operating voltage ≥100V and an operating temperature≥100 C, wherein, the dielectric body comprises a dielectric polymercomposition characterised by: a conduction transition temperature Tc, afirst activation energy Ea_(Low) for conduction in a first range oftemperatures below Tc, a second activation energy Ea_(High) forconduction in a second range of temperatures above Tc, and thedielectric polymer composition having values of Tc, Ea_(Low), andEa_(High) that provide a conductivity less than a reliability thresholdvalue of conduction for the rated operating voltage and temperature. 2.The semiconductor device of claim 1, wherein the reliability thresholdfor conduction is ≤2×10⁻¹³ S/cm.
 3. The semiconductor device of claim 1,wherein the reliability threshold for conduction is ≤5×10⁻¹⁴ S/cm. 4.The semiconductor device of claim 1, wherein the leakage is ≤3×10⁻⁸A/cm².
 5. The semiconductor device of claim 1, wherein the leakage is≤3×10⁻⁹ A/cm².
 6. The semiconductor device of claim 1, wherein the firstactivation energy Ea_(Low) is a specified first threshold activationenergy of ≤0.2 eV.
 7. The semiconductor device of claim 1, wherein thesecond activation energy Ea_(High) is a specified second thresholdactivation energy of <1 eV.
 8. The semiconductor device of claim 1,wherein Tc is greater than the rated operating temperature and Ea_(Low)has a value ≤0.2 eV that maintain the conduction below a reliabilitythreshold of ≤2×10 ⁻¹³ S/cm.
 9. The semiconductor device of claim 1,wherein Tc is less than the rated operating temperature, Ea_(Low) has avalue ≤0.2 eV, and Ea_(High) has a value ≤1 eV that maintains theconduction below a reliability threshold of ≤5×10'S/cm.
 10. Thesemiconductor device of claim 1, wherein Tc is less than the ratedoperating temperature, Ea_(Low) has a value ≤0.2 eV, and Ea_(High) has avalue ≤1 eV that maintains the conduction below a reliability thresholdof ≤2×10 ⁻¹³ S/cm.
 11. The semiconductor device of claim 1, wherein Tcis greater than the rated operating temperature and Ea_(Low) has a value≤0.2 eV that maintain the conduction below a reliability threshold of≤5×10⁻¹⁴ S/cm.
 12. The semiconductor device of claim 1, wherein thedielectric polymer composition is a dielectric epoxy composition. 13.The semiconductor device of claim 1, wherein the dielectric polymercomposition is a laminated epoxy composition.
 14. The semiconductordevice of claim 1, wherein Tc is ≥100 C.
 15. The semiconductor device ofclaim 1, wherein Tc is ≥75 C.
 16. The semiconductor device of claim 1,wherein the semiconductor die comprises a power switching device. 17.The semiconductor device of claim 1, wherein the power switching devicecomprises a lateral GaN power transistor.
 18. The semiconductor deviceof claim 1, wherein the power switching device comprises a lateral GaNe-HEMT which is rated for 100V operation.
 19. The semiconductor deviceof claim 1, wherein the power switching device comprises a lateral GaNe-HEMT which is rated for 650V operation.
 20. The semiconductor deviceof claim 1, wherein the power switching device comprises a SiC MOSFET ora Si IGBT.